This invention relates to devices for measuring two properties of an object, such as water content and density. In particular, this invention relates to such detectors using scattered electromagnetic radiation at scattering angle greater than zero degree. More particularly, this invention relates to the use of two frequencies to measure two properties of an object, with the two frequencies selected in such a manner that at one frequency both the real and imaginary parts of the dielectric constants of components of the object that are of interest are quite different, whereas at the other frequency, at least one of the real and imaginary parts of the dielectric constants of the components of the object that are of interest are relatively close in value; the complex dielectric constant of one of the object's relevant components is fairly constant for the two frequencies. This invention is particularly directed to monitoring objects that do not strongly attenuate electromagnetic radiation.
It is known that the change in the angular scattering spectrum of an object from its expected angular scattering spectrum at a particular frequency of electromagnetic radiation can be used as an indication that impurities are present in the object. U.S. Pat. No. 4,707,652, which is hereby incorporated by reference in its entirety, shows such a device, and in particular discusses its use to detect impurities in cigarettes during manufacture. However, such a device can only determine that some aspect of the object deviates from the expected norm, but cannot isolate changes in individual components of the object unless additional information is available from other sources.
In the manufacture of cigarettes, for example, it is desirable not only to be able to detect the presence of impurities in the tobacco rod being formed on a cigarette making machine, but also to be able to measure cigarette density and moisture content and particularly variation from normality during manufacture. Currently, two separate measurements using different types of monitors are needed to determine density and moisture content of the tobacco rod. Generally, the density measurement is made by beta ray attenuation.
It would be desirable to be able to provide apparatus for monitoring two components of an object simultaneously using electromagnetic radiation.
It also would be desirable to be able to provide such apparatus for objects which attenuate electromagnetic radiation by a small amount.
It further would be desirable to be able to provide such apparatus which does not use radioactive materials.